From: Con Kolivas <kernel@kolivas.org>
To: Nikita Danilov <nikita@clusterfs.com>
Subject: Re: [PATCH] mm: Implement Swap Prefetching v22
Date: Fri, 10 Feb 2006 11:08:46 +1100
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Cc: Nick Piggin <nickpiggin@yahoo.com.au>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, ck list <ck@vds.kolivas.org>,
       linux-mm@kvack.org, Nick Piggin <npiggin@suse.de>,
       Paul Jackson <pj@sgi.com>
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On Friday 10 February 2006 05:04, Nikita Danilov wrote:
> Nick Piggin writes:
>
> [...]
>
>  > > +/*
>  > > + * We check to see no part of the vm is busy. If it is this will
>  > > interrupt + * trickle_swap and wait another PREFETCH_DELAY.
>  > > Purposefully racy. + */
>  > > +inline void delay_swap_prefetch(void)
>  > > +{
>  > > +	__set_bit(0, &swapped.busy);
>  > > +}
>  > > +
>  >
>  > Test this first so you don't bounce the cacheline around in page
>  > reclaim too much.
>
> Shouldn't we have special macros/inlines for this? Like, e.g.,
>
> static inline void __set_bit_weak(int nr, volatile unsigned long * addr)
> {
>         if (!__test_bit(nr, addr))
>                 __set_bit(nr, addr);
> }
>
> ? These test-then-set sequences start to proliferate throughout the code.

Maybe.

There isn't actually a non-atomic __test_bit anyway, only a test_bit. The 
non-atomic __test_and_set_bit already exists, but that sets the bit 
regardless of what the bit was as far as I can tell.

Cheers,
Con
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